Slitting is the dividing of a single, wide strip of metal into narrower strips or slits (also called mults or strands). Some products made from slit metal stock include cans, razor blades, Venetian blinds, office furniture, automobile parts, electrical equipment, appliances, aerospace parts, medical equipment, building materials, jewelry and blanks for minting coins. Slitting is also applied to nonmetallic materials including paper, plastic, film and fiber.
Although metal slitting machines may vary in size from so-called "tabletop" slitters with small motors (used for foil to light gauge material) to those using motors of several hundred horsepower and requiring a building hundreds of feet in length, all slitting machines require essentially the same type of tooling, and vary only in the size, quantity and customization of the end use. A comprehensive review of metal slitting machinery and a discussion of many of the system parameters relevant to such machinery may be found in Rogers, J. W. and Millan, W. H., Coil Slitting, Pergamon Press (1972), the disclosure of which is incorporated herein by reference.
In general, all slitting machines have three major components: (1) a means to get the metal to the slitter--for coil slitters it is an uncoiler (also referred to as an unwinder or payoff reel); (2) a slitter head--for holding the rotary knives and associated tooling (such as spacers, stripper rings etc.) and (3) a recoiler (also referred to as a rewinder or take-up reel)--for rewinding the mults (strands).
Operators of slitting machines generally find that the actual slit width of a particular mult varies from the theoretical slit width as determined by the distance between the slitting knives positioned upon an arbor. For most metals, the actual slit width is found to be narrower than the theoretical slit width. To account for "slit width shrinkage" with such metals, operators generally adjust the position of the slitting knives to provide a theoretical slit width slightly greater than the ordered or desired slit width.
Although slit width variation is well known in the metal slitting industry, the understanding of the physical mechanisms underlying the phenomenon is incomplete. Nonetheless, certain system parameters such as the tensile strength of the metal, the thickness of the metal, the horizontal clearance between opposing knives and the slit width are known to influence the amount of variation. In that regard, practitioners often keep a journal of such system variables and the experienced slit width variation as a reference for attempting to forecast slit width variation in future runs.
Still, adjustment of knife position to account for slit width variation remains very much an art rather than a science. In the art of predicting slit width variation there are several rules of thumb, including: (1) slit width shrinkage is more pronounced in heavier gauge materials and (2) the slit width shrinkage is approximately one half of the horizontal clearance between two adjacent, opposing knives.
Given the increasingly precise mult width specifications required of metal providers, a design tool for assisting operators of slitting machinery to more accurately adjust mult width to account for slit width variation is very desirable.